1. Field of the Invention
The present invention relates to a power transmission control device for a vehicle, and more particularly, to a power transmission control device applied to a vehicle provided with an internal combustion engine and an electric motor as power sources, and also provided with a clutch.
2. Description of the Related Art
In recent years, a power transmission control device including a multiple gear ratio transmission having a plurality of gear positions and not having a torque converter, a clutch interposed between an output shaft of an internal combustion engine and an input shaft of the multiple gear ratio transmission and capable of adjusting a clutch torque (the maximum value of the torque which the clutch can transmit), and control means for controlling, depending on a travel state of a vehicle, by using actuators, the clutch torque and a gear position of the multiple gear ratio transmission has been developed (for example, see Japanese Patent Application Laid-open No. 2006-97740). This power transmission control device is also referred to as automated manual transmission (AMT).
In a vehicle equipped with the AMT, usually based on a map created in advance for prescribing a relationship between “an accelerator opening and a vehicle speed” and “a gear position to be realized”, and on current values of the accelerator opening and the vehicle speed, the gear position to be realized is determined and changed.
Further, in recent years, a so-called hybrid vehicle provided with an engine and an electric motor (an electric motor and an electric power generator) as power sources has been developed (for example, see Japanese Patent Application Laid open No. 2000-224710). In the hybrid vehicle, a configuration may be employed in which an output shaft of the electric motor is connected to any one of en output shaft of the internal combustion engine, an input shaft of a transmission, and an output shaft of the transmission.
In the following description, a driving torque of the output shalt of the internal combustion engine is referred to as “internal-combustion-engine driving torque”, and a driving torque of the output shaft of the electric motor is referred to as “electric-motor driving torque”.
In the following description, a hybrid vehicle (hereinafter referred to as “hybrid vehicle with an AMT”) having a configuration in which an AMT is installed and the output shaft of the electric motor is connected to the output shaft of the transmission is assumed. In the hybrid vehicle with the AMT, “an electric-motor travel mode” for traveling, in a state in which the clutch torque is maintained to zero, by using only the electric-motor driving torque, and “an internal-combustion-engine travel mode” for traveling, in a state in which the clutch torque is adjusted to a value larger than zero, by using only the internal-combustion-engine driving torque or “both the internal-combustion-engine driving torque and the electric-motor driving torque” can be selectively realized.
In the electric-motor travel mode, the electric-motor driving torque is transmitted, without intermediation of the multiple gear ratio transmission, from the output shaft of the electric motor to the output shaft of the transmission (thus, to drive wheels). As a result, based on the above-mentioned map, the necessity of sequentially changing “the gear position to be realized” is low. In addition, when “the gear position to be realized” is changed, an action sound is unavoidably generated by the change. Due to this action sound, occupants can feel a sense of discomfort.